Radio wave-transmitting wavelength-selective plate and method for producing same

ABSTRACT

The present invention relates to a radio wave-transmitting, wavelength-selective plate, which is characterized in that a layer composed of Ag fine particles is formed and that the central portions of the Ag fine particles contain an alloy (Ag alloy) formed of Ag and a metal which forms a homogeneous solid solution with Ag (hereinafter referred to as a homogeneous solid solution metal).

BACKGROUND OF THE INVENTION

The present invention relates to a method for producing a radiowave-transmitting wavelength-selective plate that can efficientlytransmit radio waves and visible light rays arriving at window glassesof buildings, automobiles and the like and that exhibits a sufficientheat insulation by reflecting heat rays of the sun.

In recent years, window glasses covered with conductive thin films orwindow glasses having films coated with conductive thin films have begunto prevail, for the purpose of shielding solar radiation.

The application of such window glasses to high buildings reflects radiowaves of TV frequency band and causes the occurrence of ghost on the TVscreen. Furthermore, it becomes difficult to receive satellite broadcastusing an indoor antenna.

Furthermore, in case that they were used as residential window glassesor automotive window glasses, the communication with mobile phones waslikely to become difficult, and it became a cause to lower the gain ofan indoor antenna or glass antenna formed on vehicular window glass.

Under such condition, it is now conducted to coat a glass substrate witha transparent heat ray reflecting film of a relatively high electricresistance to transmit a part of the visible light rays and to reducethe radio wave reflection to prevent radio interference.

For example, in the case of a glass with a conductive film, it is knownto prevent radio interference by partitioning the conductive film coatedon a glass substrate such that the length of the conductive film that isparallel with the field direction of the incident radio wave is made tobe 1/20 or less times the radio wave wavelength (see Japanese Patent No.2620456).

Although the above method of coating thereon a transparent heat rayreflecting film of a relatively high electric resistance can preventradio interference by reducing the radio wave reflection, the heat rayshielding performance was not sufficient, and it was problematic interms of the life amenity.

Furthermore, a method of partitioning a conductive film is disclosed inJapanese Patent Laid-open Publication 2000-281388. Since the partitionlength is much longer than the wavelengths of the visible light and nearinfrared light occupying a most part of the sun light, all of theselights are reflected. Although there is obtained a radio-transmitting,wavelength-selective screen glass that prevents radio interference andhas a sufficient solar radiation shielding performance, there is aproblem of not being capable of maintaining the visible lighttransmission. Furthermore, in a large window having an opening size of 2m×3 m, for example, it is necessary to cut a conductive film to 1/20 ofthe wavelength (about 25 mm) of satellite broadcast, at least to 1.25 mmsquares, preferably 0.5 mm squares, in order to transmit satellitebroadcast waves. It is necessary to take a long time to cut a large-areaconductive film into such small segments by means of, for example, anyttrium-aluminum-garnet laser. Thus, it had problems such as beingunrealistic.

Thus, the present inventors and others proposed a radiowave-transmitting, wavelength-selective plate in which fine particlescomposed of Ag are formed on a transparent substrate (see JapanesePatent Laid-open Publication 2000-281388).

There was a trouble that spectral reflectance becomes low in the entirewavelength region by shifting a wavelength (hereinafter abbreviated asresonance wavelength) at which spectral reflectance reaches a maximum toa range of 700 nm to 1500 nm, in a radio wave-transmitting,wavelength-selective glass in which granular Ag is formed on atransparent substrate, in order to increase a near infrared shieldingcoefficient (Es) defined in the formula (1), as disclosed in JapanesePatent Laid-open Publication 2000-281388.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a radiowave-transmitting, wavelength-selective plate that reduces reflectanceto radio waves of respective frequency bands of TV broadcast, satellitebroadcast and mobile phone, that has sufficient solar radiationshielding performance and visible light transmission, and that ispreferable as automotive window glass and architectural window glass.

In a radio wave-transmitting, wavelength-selective plate where Ag islaminated on a transparent substrate, a radio wave-transmitting,wavelength-selective plate of the present invention is a radiowave-transmitting, wavelength-selective plate, which is characterized inthat a layer composed of Ag fine particles is formed and that a Ag alloyformed of Ag and a homogeneous solid solution metal is contained in thecentral portion of the Ag fine particles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically showing the Ag fine particlestructure; and

FIG. 2 is a SEM image of a granular Ag alloy formed on a transparentsubstrate.

DETAILED DESCRIPTION

According to the present invention, it is possible to provide a radiowave-transmitting, wavelength-selective plate that reduces reflectanceto radio waves of respective frequency bands of TV broadcast, satellitebroadcast and mobile phone, that has sufficient solar radiationshielding performance and visible light transmission, and that ispreferable as automotive window glass and architectural window glass.

As a transparent substrate used in the present invention, it is possibleto use a glass substrate, transparent ceramic substrate, heat-resistant,transparent plastic substrate or the like. In the case of using a radiowave-transmitting, wavelength-selective plate of the present inventionfor architecture and vehicular opening, glass substrate is desirable.Depending on the place for use or the like, it is preferable to selectglass substrate, transparent ceramic substrate, heat-resistanttransparent plastic substrate, or the like.

A mixed film (hereinafter referred to as Ag mixed film) composed of Agand a homogeneous solid solution metal is formed on a transparentsubstrate. By heating the Ag mixed film, a granular Ag alloy of apredetermined number is formed on the transparent substrate by atwo-dimensional dispersion. FIG. 2 is a photograph (hereinafter referredto as SEM image) by the observation of a granular Ag alloy prepared inExample with a field emission type scanning electron microscope(FE-SEM).

Furthermore, an Ag film composed of only Ag is laminated on thetransparent substrate having the granular Ag alloy formed thereon. Afterlaminating the Ag film on the granular Ag alloy, a second heatingtreatment is conducted to form a portion composed of only Ag on thesurface and the surrounding of the granular Ag alloy and to form Ag fineparticles of which central portion is composed of Ag and the homogeneoussolid solution metal. FIG. 1 schematically shows Ag fine particles 1formed on transparent substrate 4. Central portion 3 of Ag fineparticles 1 is composed of an alloy of Ag and a homogeneous solidsolution metal, and its surrounding is composed of only Ag.

The shape of the Ag fine particles is hemispherical, of a string ofdomes, flat, flake-like or needle-like or the like, as well as dome-likeshown in FIG. 1. In view of optical performance, the shape is preferablyhemispherical, dome-like, flat or flake-like.

The present invention makes it easy to control the Ag fine particleshape shown in FIG. 1. As a result, a radio wave-transmitting,wavelength-selective plate of the present invention can shift resonancewavelength to a range of 700 nm-1500 nm of a large near infrared rayshielding coefficient, thereby obtaining a radio wave-transmitting,wavelength-selective plate having superior heat insulation.

It is preferable that the number of the Ag alloy granules per unit areais controlled by the film thickness of the Ag mixed film. Furthermore,it is preferable that the particle diameter of the Ag fine particles iscontrolled by the film thickness of the Ag film that is laminated on thegranular Ag alloy.

As the homogeneous solid solution metal, it is possible to use Pd, Auand the like. By adding a metal having a melting point higher than Ag asthe homogeneous solid solution metal, it becomes possible to reduce arate at which Ag fine particles are formed.

At the second heating, the granular Ag alloy of the central portion actsas a nucleus, and it is possible to adjust the rate at which the Ag fineparticles are formed, by the difference in travel speed between Ag andthe homogeneous solid solution metal and by the amount of thehomogeneous solid solution metal added. Therefore, it is desirable touse one having a melting point higher than that of Ag, as thehomogeneous solid solution metal. Furthermore, it is desirable to selecta homogeneous solid solution metal having an atomic weight greater thanthat of Ag, since it brings about an effect of reducing the rate atwhich the Ag fine particles are formed and since it becomes easy tocontrol the shape (particle diameter L and height H of FIG. 1) of the Agfine particles.

In the case of selecting a homogeneous solid solution metal having amelting point higher than that of Ag, it is necessary to form the Agfine particles by a heating lower than softening point of thetransparent substrate. Therefore, there is an upper limit of the amountof the homogeneous solid solution metal added.

That is, in general, in case that meting point of metal is expressed byabsolute temperature, the metal on the transparent substrate startsdiffusion on the transparent substrate surface at a temperature that is0.3 times the melting point. Therefore, in case that melting point ofthe homogeneous solid solution metal is higher than that of Ag, it ispossible to add the homogeneous solid solution metal until a value thatis 0.3 times the melting point of the Ag alloy becomes equal to thesoftening point of the transparent substrate.

A preferable particle height H of the Ag fine particles is 10 nm to 500nm, but it is not limited to these. The particle diameter L of the Agparticles is preferably a size of 100 nm to 0.5 nm.

The film thicknesses of the Ag mixed film and the Ag film are preferablyin a range of 5 nm to 1 μm. If they are less than 5 nm, the Ag filmturns to have an island-like shape and is not formed uniformly. Thus, itis not preferable. If it exceeds lam, it becomes difficult to form agranular shape at a heating temperature lower than softening point ofthe transparent substrate. Thus, it is not preferable.

The method of forming the Ag mixed film and the Ag film is notparticularly limited. It is possible to use a film forming method suchas sputtering, vacuum deposition, CVD method, and ion plating. Inparticular, DC magnetron sputtering is preferable from the points ofhomogeneity of the formed layer and productivity. It is possible to formthe Ag mixed film by using a means of adding a homogeneous solidsolution metal in the chip form to an Ag target member or by using atarget composed of an alloy of Ag and homogeneous solid solution metal.

The method of heating the Ag mixed film and the Ag film can be conductedby a method such as resistance heating, gas burning heating, laser orelectron beam irradiation, or induction heating In the case of using aheat resistant, transparent plastic as the transparent substrate, aheating by a laser beam that is almost not absorbed by the transparentsubstrate and an induction heating that can selectively heat only theconductive material are preferable heating methods.

Regarding the heating condition, it is preferable that the heatingtemperature is 150° C. or higher and a temperature, at which thetransparent substrate does not soften, or lower.

In the case of heating the transparent substrate formed with the Agmixed film and the Ag film, for example, in a heating furnace, 150° C.or higher is preferable in order to form the granular Ag alloy and theAg fine particles in several hours.

If the temperature of the transparent substrate exceeds softening point,particularly in the case of using an oxide glass for the transparentsubstrate, Ag atoms diffuse in the transparent substrate. With this,wavelength selectivity by the reflection of electromagnetic waves lowersextremely.

In case that the Ag film or Ag mixed film is subjected to an irradiationwith a beam such as laser or electron beam or to induction heating, itis possible to selectively heat the Ag film or Ag mixed film withoutheating the transparent substrate. Therefore, the upper limit of theheating temperature can be set to the boiling point of Ag, 2212° C.

The heating time is preferably from several seconds to several hours inthe case of resistance heating and gas burning heating and frommicroseconds to several seconds in the case of beam irradiation such aslaser or electron beam or induction heating. After the heating, it maybe cooled down by self-cooling or compulsory cooling such as airblowing.

Plasma frequency, at which extinction coefficient of Ag becomesinfinitesimal, resides in a wavelength range of the ultraviolet regionthat is close to the visible light region. Therefore, transparency ofvisible light rays can be ensured by controlling the thickness of the Agparticles and the thickness of the dielectric layer film.

Furthermore, a radio wave-transmitting, wavelength-selective plate ofthe present invention controls the particle diameter L, the number,distribution and the like of the Ag fine particles by the thickness ofthe Ag mixed film, the thickness of the Ag film and the heatingcondition and selectively reflects near infrared rays. The number may betaken as occupancy a real ratio of the substrate surface, relative tothe particle diameter L.

In order to selectively reflect near infrared rays, it is preferablethat the near infrared shielding coefficient (Es) defined in thefollowing formula (1) is 0.3 or greater. To make it 0.3 or greater, itis preferable to control the number of the Ag alloy granules and theparticle diameter of the Ag fine particles such that the maximum valueof the spectral reflectance of the radio wave-transmittingwavelength-selective plate is in a wavelength range of 600 nm to 1500nm, to adjust the particle diameter L of the Ag fine particles to 100 nmto 0.5 mm, and to adjust the occupancy a real ratio to 0.2-0.8.$\begin{matrix}{E_{s} = \frac{\sum\limits_{\lambda = 680}^{1800}\lbrack {{R_{dp}(\lambda)}{I_{sr}(\lambda)}} \rbrack}{\sum\limits_{\lambda = 680}^{1800}\lbrack {I_{sr}(\lambda)} \rbrack}} & (1)\end{matrix}$where λ is a wavelength of an electromagnetic wave incident on the filmsurface,

R_(dp) is a reflectance of the film surface at the wavelength λ, andI_(sr) is an intensity of solar radiation at the wavelength λ when anair-mass is 1.5.

If the occupancy a real ratio of the Ag fine particles is less than 0.2,the average distance between the Ag particles becomes two times theparticle diameter or greater. With this, the mutual interference betweenthe particles becomes small, and it is not possible to obtain a radiowave-transmitting, wavelength-selective plate having an effective nearinfrared shielding coefficient. In case that the particle diameter ofthe Ag fine particles is less than 100 nm, the maximum value of thespectral reflectance turns to be 600 nm or less.

If the occupancy a real ratio exceeds 0.8, almost the Ag fine particlesturn to be in a cluster form, thereby loosing the wavelength-selectivefunction to transmit radio waves. Even in case that the particlediameter L of the Ag fine particles exceeds 0.5 mm, thewavelength-selective function to transmit radio waves is lost.

It is possible to determine the occupancy a real ratio of the Ag fineparticles, for example, by an observation with a field emission typescanning electron microscope (FE-SEM) in the direction of normal line ofthe transparent substrate to obtain an SEM image, then by subjecting theSEM image to a binarization through an image processing of the Ag fineparticles and the surface of the transparent substrate on which the Agfine particles are not present, and then by dividing the total area ofthe Ag fine particles by the total area of the SEM image.

The particle diameter L of the Ag fine particles may be obtained bydetermining the number of the Ag fine particles by an image obtained bythe binarization of the SEM image and then by dividing the total area ofthe Ag fine particles by that number. The obtained area may be definedas being of a circle of the same area, and the diameter of the circlemay be defined as the particle diameter of the Ag fine particles.

Therefore, for example, in case that the Ag fine particles are in adome-like shape, the particle diameter L corresponds to the diameter ofthe bottom surface of the dome.

In a radio wave-transmitting, wavelength-selective plate of the presentinvention, it is preferable to form a dielectric layer as an underlayerand/or top layer of the Ag fine particles.

In case that a dielectric layer is formed as an underlayer of the Agfine particles, the Ag mixed film is formed after forming the dielectriclayer on the transparent substrate surface.

In case that a dielectric layer is formed as a top layer of the Ag fineparticles, the dielectric layer is formed on the Ag fine particles afterforming the Ag fine particles.

As the dielectric layer, it is possible to use a nitride of either metalof Al, Si, Ti, Ta, Ge, In, W, V, Mn, Cr, Ni and stainless steel; anoxide of either metal of Al, Si, Zn, Sn, Ti, Ta, Ge, In, W, V, Mn, Cr,Ni and stainless steel, or a laminate of these.

In particular, since nitrides of metals of Al and Si and oxides ofmetals of Al, Si, Zn, Sn, Ti, Ta and In are colorless and transparent,they are suitable for architectural and vehicular window glasses thatdemand a radio wave-transmitting, wavelength-selective plate having ahigh visible light transmittance.

If the Ag fine particles are coated with a dielectric layer, the visiblelight transmittance is increased by an interaction with a dielectriclayer formed on the transparent substrate, and it acts as a protectivefilm for the deterioration prevention of the Ag granular layer and thelike. Thus, it is more preferable. As a dielectric layer used in thiscase, nitrides of Al and Si, oxides of Al, Si, Zn, Sn, Ti, Ta and In, orlaminates of these are desirable.

As a method for forming the dielectric layer, sputtering, vacuumdeposition, CVD method, ion plating and the like are used. Inparticular, DC magnetron sputtering is more preferable from the pointsof homogeneity and productivity of the formed layer.

In the following, examples of the present invention are described. Thepresent invention is not limited to these.

EXAMPLE 1

A radio wave-transmitting, wavelength-selective plate of the presentinvention was produced by the following procedure. A float glass platewas used as the transparent substrate.

1) Firstly, a washed float glass plate of a thickness of 3 mm was putinto a DC magnetron sputtering apparatus, followed by exhaust until thedegree of vacuum reaches 2×10⁻⁴ Pa to 4×10⁻⁴ Pa. The distance betweenthe target and the glass substrate was set to 90 mm.

2) Then, four of Pd chips (rectangular parallelopiped of 10 mm×10 mm×1mm) were equidistantly placed on an erosion region of an Ag target(diameter: 152 mm; thickness: 5 mm). An electric power of DC 30 W wasapplied to this target to make it discharge, thereby forming an Ag-Pdmixed film of a film thickness of 13 nm. During the film formation, thepressure of Ar gas was controlled to 1 Pa.

3) Then, the transparent substrate having thereon the Ag mixed film washeated for 5 min in a thermostatic oven of an ambient temperature of500° C. Then, it was taken out of the oven for self-cooling, therebyforming a granular Ag alloy on the surface of the transparent substrate.

4) Then, an electric power of DC 30 W was applied to the Ag target(diameter: 152 mm; thickness: 5 mm) to make it discharge, therebylaminating an Ag film of a film thickness of 13 nm on the granular Agalloy. Ar gas (pressure: 1 Pa) was used as the atmosphere during thefilm formation.

5) Then, that with the Ag film laminated thereon was heated for 5 min ina thermostatic oven of an ambient temperature of 450° C. Then, it wastaken out of the oven for self-cooling, thereby forming Ag fineparticles on the glass surface of the substrate.

6) Then, the steps of 4) and 5) were further repeated two times, therebyincreasing the particle diameter L and the height H of the Ag fineparticles.

Spectral reflectance and spectral transmittance of the thus obtainedradio wave-transmitting, wavelength-selective plate were measured in awavelength range of 300-2500 nm using U-4000 type automatedspectrophotometer made by Hitachi Ltd. Furthermore, the measured valuewas substituted in the formula (1), thereby determining the nearinfrared shielding coefficient. The results are shown in Table 1.

As a result, there was obtained a good wavelength-selective plate havinga large near-infrared shielding coefficient of 0.51 at a resonancewavelength of 720 nm and a visible light transmittance of 15%.

EXAMPLE 2

A radio wave-transmitting, wavelength-selective plate was prepared byforming Ag fine particles on the transparent substrate surface byrepeating Example 1, except in that the operations of 4) and 5) ofExample 1 were repeated five times. As a radio wave-transmitting,wavelength-selective plate of the present example, there was obtained agood wavelength-selective plate having a very large value of 0.61 innear infrared shielding coefficient at a resonance wavelength of 900 nmand a slightly decreased visible light transmittance of 13%.

COMPARATIVE EXAMPLE 1

In the present comparative example, fine particles composed of only Agwere formed on a transparent substrate by the following procedures usingthe same float glass plate as that of Examples 1 and 2.

1) Firstly, a washed float glass plate of a thickness of 3 mm was putinto a DC magnetron sputtering apparatus, followed by exhaust until thedegree of vacuum reaches 2×10⁻⁴ Pa to 4×10⁻⁴ Pa. The distance betweenthe target and the glass substrate was set to 90 mm.

2) Then, an electric power of DC 30 W was applied to the Ag target(diameter: 152 mm; thickness: 5 mm) to make it discharge, therebyforming an Ag film of a film thickness of 25 nm. During the filmformation, the pressure of Ar gas was controlled to 1 Pa.

5) Then, the transparent substrate with the Ag film formed thereon washeated for 5 min in a thermostatic oven of an ambient temperature of500° C. Then, it was taken out of the oven for self-cooling, therebyforming granular Ag on the surface of the transparent substrate.

Spectral reflectance and spectral transmittance of the thus obtained onewere measured in a wavelength range of 300-2500 nm using U-4000 typeautomated spectrophotometer made by Hitachi Ltd. Furthermore, themeasured value was substituted in the formula (1), thereby determiningthe near infrared shielding coefficient. The results are shown in Table1.

In the product of Comparative Example 1, the resonance wavelengthshifted from the visible region to 900 nm, and the visible lighttransmittance increased to 52%. However, the near infrared shieldingcoefficient was as small as 0.3, and one having a high near-infraredshielding coefficient was not obtained. TABLE 1 Resonance Visible LightOccupancy Wavelength Near Infrared Transmittance Area Ratio (nm)Shielding Coef. (%) Ex. 1 0.47 720 0.51 15 Ex. 2 0.57 900 0.61 13 Com.0.25 900 0.30 52 Ex. 1

As shown in Table 1, there were obtained in Examples 1 and 2 ones havinghigh near infrared shielding coefficients by shifting the resonancewavelengths to a range of 700 nm to 1500 nm. In contrast, in the case ofComparative Example 1, one having a high near-infrared shieldingcoefficient was not obtained.

1. A radio wave-transmitting, wavelength-selective plate having Aglaminated on a transparent substrate, characterized in that a layerwherein Ag fine particles are dispersed by a heat treatment is formedand that a central portion of the Ag fine particles contains an alloy(hereinafter referred to as Ag alloy) formed of Ag and a metal forming ahomogeneous solid solution (hereinafter referred to as homogeneous solidsolution metal) with Ag.
 2. A radio wave-transmitting,wavelength-selective plate according to claim 1, characterized in that avalue obtained by multiplying the highest temperature of melting pointof the Ag and melting point of the Ag alloy by 0.3 is lower thansoftening point of the transparent substrate.
 3. A radiowave-transmitting, wavelength-selective plate according to claim 1,characterized in that average particle diameter L of the Ag fineparticles is 100 nm to 0.5 mm and that a proportion of an area coveredwith the Ag fine particles on a surface of the transparent substrate isin a range of 0.2 to 0.8.
 4. A radio wave-transmitting,wavelength-selective plate according to claim 1, characterized in thatthe maximum value of light ray reflectance is in a wavelength range of600 nm to 1500 nm.
 5. A radio wave-transmitting, wavelength-selectiveplate according to claim 1, characterized in that a dielectric layer isformed as an underlayer and/or top layer of a layer composed of the Agfine particles.
 6. A radio wave-transmitting, wavelength-selective plateaccording to claim 1, characterized in that an electromagnetic wave isincident on a surface on which a layer composed of the Ag fine particlesis formed and that a near infrared shielding coefficient (Es) defined inthe formula (1) is 0.3 or greater, $\begin{matrix}{E_{s} = \frac{\sum\limits_{\lambda = 680}^{1800}\lbrack {{R_{dp}(\lambda)}{I_{sr}(\lambda)}} \rbrack}{\sum\limits_{\lambda = 680}^{1800}\lbrack {I_{sr}(\lambda)} \rbrack}} & (1)\end{matrix}$ where λ is a wavelength of an electromagnetic waveincident on the film surface, R_(dp) is a reflectance of the filmsurface at the wavelength λ, and I_(sr) is an intensity of solarradiation at the wavelength λ when an air-mass is 1.5.
 7. A method forproducing a radio wave-transmitting, wavelength-selective plateaccording to claim 1, characterized in that a mixed film, in which theAg and the homogeneous solid solution metal are mixed together, isformed on a transparent substrate, followed by a heat treatment of themixed film, thereby forming a layer of the Ag fine particles on thetransparent substrate.
 8. A method for producing a radiowave-transmitting, wavelength-selective plate according to claim 7,characterized in that the number of the Ag fine particles per unit areais controlled by a film thickness of Ag and/or a film thickness of ametal forming a homogeneous solid solution and/or a film thickness ofthe mixed film.
 9. A method for producing a radio wave-transmitting,wavelength-selective plate according to claim 7, characterized in thatan Ag layer is laminated on the Ag fine particles on the surface of thetransparent substrate, followed by a heating treatment, thereby formingfine particles in which the Ag fine particles are surrounded by only Ag.10. A method for producing a radio wave-transmitting,wavelength-selective plate according to claim 7, characterized in that aparticle diameter and an occupancy a real ratio of the Ag fine particlesare controlled by the film thickness of the Ag layer and/or the numberof the lamination of the Ag layer.
 11. A method for producing a radiowave-transmitting, wavelength-selective plate according to claim 7,characterized in that at least one method selected from resistanceheating, gas burning heating, laser irradiation, electron beamirradiation and induction heating is used as a heating method in theheating treatment.
 12. A method for producing a radio wave-transmitting,wavelength-selective plate according to claim 7, characterized in thattemperature of the transparent substrate in the heating treatment is150° C. or higher and is lower than softening point of the transparentsubstrate.
 13. A method for producing a radio wave-transmitting,wavelength-selective plate according to claim 7, characterized in thatthe mixed film, in which Ag and the homogeneous solid solution metal aremixed together, and the Ag film are formed by a DC magnetron sputtering.14. A method for producing a radio wave-transmitting,wavelength-selective plate according to claim 4, characterized in thatthe dielectric layer is formed by a DC magnetron sputtering.